A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disk having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head that is positioned over a specific location of a disk by an actuator. A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. A write head makes use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
Increasing areal density, a measure of the quantity of information bits that can be stored on a given area of disk surface, is one of the ever-present goals of HDD design evolution. As areal density increases, the read/write head generally needs to fly closer and closer to the disk surface. Flying height control systems are often used to fly the read/write head as close as possible to the magnetic-recording disk for effective operation of the head. Typically, such systems gently urge the head area of the slider toward the disk until contact is made (“touchdown”) at which point the slider is urged away from the disk (“back-off”). However, the act of contacting the disk causes mechanical wear of the head which, over time, often leads to operational degradation and eventually failure. Preferably, a touchdown event is sharp, sensitive, repeatable, and gentle so as to avoid wear. Therefore, reliable touchdown and back-off events are critical to the performance of the hard disk drive as it is used to set the critical sub-nanometer clearance air gap between the disk and the head.
Historically, the reduction in overall head-disk interface roughness has been considered important to meeting head-disk spacing goals. Flying instabilities were combated with the innovative use of a thermal flying height control (“TFC”) heater in the heads. TFC is utilized to create a slider bulge in the area of the head, and thus reduces the overall area of interaction of the head and disk, and hence the total destabilizing forces arising from atomically smooth surfaces in close proximity. However, as disk and head designers strive to reach even lower roughness in order to meet future head-disk spacing goals, head instabilities at touchdown can manifest even for TFC sliders, which have a very small area of interaction at the head disk interface.
Any approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.